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Дата изменения: Thu May 17 13:42:51 2007
Дата индексирования: Wed Dec 26 09:18:04 2007
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Journal "Peremennye Zvezdy"
Peremennye Zvezdy


Peremennye Zvezdy (Variable Stars) 26, No. 2, 2006

Received 19 February; accepted 25 March.

Article in PDF

Photometric elements and stellar parameters for the contact binary RZ UMi

Van Cauteren, P.1,3; Lampens, P.2; Wils, P.3

  1. Beersel Hills Observatory, Laarheidestraat 166, B-1650 Beersel, Belgium, email: PaulVanCauteren@skynet.be

  2. Koninklijke Sterrenwacht van België, B-1180 Brussel, Belgium, email: Patricia.Lampens@oma.be

  3. Vereniging Voor Sterrenkunde, Belgium, email: Patrick.Wils@cronos.be

The contact binary RZ UMi (= SVS 2310 = GSC 4642-0832 = 1RXS J145418.3+864338; ; ) was discovered by Goranskij (1982), who also attributed it to the W UMa class with a period of 0.33735283 days. No other observations of this star have been published since.

We therefore re-observed RZ UMi at Beersel Hills Observatory on nine nights between May 2001 and March 2003. The instrument used was a 0.4 m Newtonian telescope, equipped first with a SBIG ST7E CCD camera (2001-2002) and later with a ST10 XME camera (2003). The 2001 observations are unfiltered. From 2002 onwards, a filter according to the specifications of Bessell (1995) was used. The exposure times varied between 120 and 180 seconds. All images were reduced with the aperture photometry procedure of the Mira AP software package1 and darkframed and flatfielded according to standard procedures.

The brightness of the variable was measured with respect to GSC 4642-0777 (GSC average photographic magnitude 14.3), while GSC 4642-0752 (mag. 14.4) and GSC 4642-0833 (mag. 15.1) served as check stars. RZ UMi has magnitude 12.9 according to the GSC 1.2, while its instrumental magnitude with respect to the comparison star averaged . For the check stars we found and respectively, with nightly standard deviations on the order of 004 and 007.

The new times of minima determined by fitting a second degree polynomial through the data around the observed minimum are given in Table 1. The table also includes a normal minimum derived from data from the Northern Sky Variability Survey (NSVS; Wozniak et al., 2004). The O-C1 values are with respect to ephemeris provided by Goranskij (1982), and the E and O-C2 values are listed with respect to the ephemeris derived below.

Table 1: Observed times of minimum.
HJD Type O-C1 E    O-C2 Filter
2451442.659  I -0.091  -2750    -0.007  NSVS
2452052.4248 II -0.0906 -942  .5 0.0000 None
2452370.3769 I -0.0936 0    0.0003 V
2452371.3888 I -0.0938 3    0.0001 V
2452372.4019 I -0.0927 6    0.0012 V
2452386.4015 II -0.0933 47  .5 0.0008 V
2452720.3774 II -0.0967 1037  .5 0.0007 V

From these minima and the computed time of minimum given by Goranskij (1982), the following improved ephemeris was deduced:

Min = HJD 2452370.3766 + 0.33734941d x E.
± 0.0008 ± 0.00000011

Within the accuracy of Goranskij's data, the orbital period is found to be constant.

The parameters of the system were derived using the Wilson-Devinney (WD) code (Wilson, 1998). The average temperature of the primary star was assumed to be  K, from the rough period-colour relation for W UMa stars (Eggen, 1967). Values for gravity darkenings (0.32) and bolometric albedos (0.5) typical for contact binaries were assumed. Limb darkening coefficients have been taken from the tables by Van Hamme (1993). Best fits were then derived with the temperature of the secondary (), the inclination (), and the surface potential and the relative monochromatic luminosity of the primary star as free parameters, assuming different values of the mass ratio . These calculations showed that any mass ratio between 0.8 and 2.2 fitted the data almost equally well (see Fig. 1). The value for the temperature of the secondary star stays almost constant at  K throughout this interval, while the value for the inclination increases from (for ) to (for ).

Fig. 1. Sum of squared residuals of WD fit for different values of the mass ratio .

Fig. 2 shows the phased light curve (2002-2003) superposed on the model fit with , as well as the residuals after subtraction of the model. The remaining scatter after subtraction is of the order of 004. Differential data are given in Table 2.

Acknowledgements: The authors are pleased to acknowledge Prof. R. Wilson (University of Florida) for providing the Wilson-Devinney code. P. Lampens acknowledges support from the Fund for Scientific Research (FWO) - Flanders (Belgium) through project G.0178.02. P. Van Cauteren is grateful to the Royal Observatory of Belgium for putting at his disposal material acquired by the same FWO project. A part of these data were acquired with equipment purchased thanks to a research fund financed by the Belgian National Lottery (1999).

References:

Bessell, M.S., 1995, CCD Astronomy, 2, 20

Eggen, O.J., 1967, Mem. R. Astron. Soc., 70, 111

Goranskij, V.P., 1982, Peremennye Zvezdy Prilozhenie, 4:20, 169

Van Hamme, W., 1993, Astron. J., 106, 2096

Wilson, R.E., 1998, Computing Binary Star Observables, (Reference manual to the Wilson-Devinney program), Department of Astronomy, University of Florida, Gainesville, FL, 1998 edition

Wozniak, P.R., Vestrand, W.T., Akerlof, C.W., Balsano, R., Bloch, J., Casperson, D., Fletcher, S., Gisler, G., Kehoe, R., Kinemuchi, K., Lee, B.C., Marshall, S., McGowan, K.E., McKay, T.A., Rykoff, E.S., Smith, D.A., Szymanski, J., Wren, J., 2004, Astron. J., 127, 2436

Fig. 2. Phased light curve of RZ UMi (upper panel), and residuals after WD fit (lower panel)

Table 2: Differential instrumental magnitudes of RZ UMi with respect to GSC 4642-0777.
HJD-2452000 HJD-2452000 HJD-2452000
370.3697 -1.595 371.4647 -2.214 386.3425 -2.239
370.3718 -1.600 371.4668 -2.213 386.3442 -2.262
370.3739 -1.575 371.4702 -2.233 386.3459 -2.190
370.3761 -1.543 371.4723 -2.195 386.3475 -2.161
370.3782 -1.518 371.4744 -2.225 386.3492 -2.225
370.3803 -1.581 371.4766 -2.179 386.3508 -2.187
370.3824 -1.565 371.4787 -2.209 386.3525 -2.204
370.3845 -1.630 371.4808 -2.207 386.3542 -2.186
370.3867 -1.673 371.4829 -2.193 386.3558 -2.110
370.3888 -1.727 371.4851 -2.188 386.3575 -2.115
370.3909 -1.734 371.4872 -2.199 386.3592 -2.166
370.3930 -1.771 371.4893 -2.168 386.3608 -2.067
370.3952 -1.903 371.4914 -2.193 386.3625 -2.040
370.3973 -1.923 371.4936 -2.197 386.3641 -2.096
370.3994 -1.895 371.4957 -2.174 386.3658 -2.088
370.4015 -1.963 371.4978 -2.226 386.3675 -2.054
370.4037 -1.967 371.4999 -2.172 386.3691 -2.088
370.4058 -1.911 371.5020 -2.152 386.3708 -2.039
370.4079 -2.046 371.5042 -2.203 386.3725 -2.019
370.4100 -1.996 371.5063 -2.164 386.3741 -1.963
370.4122 -2.020 371.5084 -2.142 386.3758 -2.037
370.4143 -2.081 371.5105 -2.179 386.3774 -1.973
370.4164 -2.131 371.5127 -2.118 386.3791 -1.963
370.4185 -2.148 371.5148 -2.114 386.3808 -1.875
370.4207 -2.130 371.5169 -2.091 386.3824 -1.912
370.4228 -2.087 371.5191 -2.096 386.3841 -1.796
370.4249 -2.135 371.5212 -2.062 386.3857 -1.833
370.4270 -2.168 371.5233 -2.070 386.3874 -1.774
370.4292 -2.171 371.5254 -2.039 386.3891 -1.749
370.4313 -2.202 371.5275 -2.027 386.3907 -1.703
370.4334 -2.143 371.5297 -1.991 386.3924 -1.702
370.4355 -2.202 371.5318 -1.967 386.3941 -1.617
370.4377 -2.160 371.5339 -1.947 386.3957 -1.647
370.4398 -2.225 371.5361 -1.916 386.3974 -1.652
370.4419 -2.190 371.5382 -1.873 386.3990 -1.619
370.4440 -2.251 371.5403 -1.797 386.4007 -1.603
370.4462 -2.239 371.5424 -1.796 386.4024 -1.646
370.4483 -2.225 371.5445 -1.732 386.4040 -1.568
370.4504 -2.235 371.5467 -1.681 386.4057 -1.606
370.4525 -2.192 371.5488 -1.666 386.4073 -1.641
370.4554 -2.191 372.3188 -2.150 386.4090 -1.656
370.4575 -2.202 372.3209 -2.218 386.4107 -1.691
370.4597 -2.204 372.3230 -2.152 386.4123 -1.703
370.4618 -2.191 372.3251 -2.148 386.4140 -1.738
370.4639 -2.249 372.3273 -2.150 386.4157 -1.801
370.4660 -2.200 372.3294 -2.139 386.4173 -1.854
370.4681 -2.227 372.3315 -2.249 386.4190 -1.867
370.4703 -2.203 372.3337 -2.181 386.4206 -1.908
370.4724 -2.216 372.3358 -2.156 386.4233 -1.912

Table 2: Continued
HJD-2452000 HJD-2452000 HJD-2452000
370.4745 -2.170 372.3379 -2.217 386.4254 -1.947
370.4767 -2.211 372.3400 -2.143 386.4275 -1.970
370.4788 -2.212 372.3421 -2.083 386.4296 -1.970
370.4809 -2.196 372.3443 -2.141 386.4318 -1.977
370.4830 -2.173 372.3464 -2.098 386.4339 -2.004
370.4852 -2.173 372.3485 -2.082 386.4360 -2.011
370.4873 -2.135 372.3506 -2.149 386.4381 -2.063
370.4894 -2.135 372.3528 -2.119 386.4403 -2.095
370.4915 -2.188 372.3549 -2.079 386.4424 -2.118
370.4936 -2.126 372.3570 -2.132 386.4445 -2.098
370.4958 -2.129 372.3591 -2.072 386.4466 -2.079
370.4979 -2.146 372.3613 -2.036 386.4488 -2.199
370.5000 -2.108 372.3634 -2.085 386.4509 -2.159
371.3394 -2.170 372.3655 -2.005 386.4530 -2.118
371.3412 -2.099 372.3676 -2.001 386.4551 -2.173
371.3430 -2.091 372.3719 -2.002 386.4573 -2.174
371.3448 -2.124 372.3740 -1.895 720.3325 -2.238
371.3465 -2.152 372.3761 -1.936 720.3340 -2.215
371.3483 -2.083 372.3783 -1.883 720.3354 -2.180
371.3501 -2.066 372.3804 -1.857 720.3369 -2.174
371.3519 -2.061 372.3825 -1.839 720.3383 -2.213
371.3536 -2.085 372.3846 -1.796 720.3398 -2.163
371.3554 -2.039 372.3868 -1.747 720.3412 -2.129
371.3572 -2.013 372.3889 -1.705 720.3427 -2.167
371.3590 -2.024 372.3910 -1.670 720.3441 -2.179
371.3607 -2.003 372.3931 -1.618 720.3455 -2.144
371.3625 -1.955 372.3953 -1.606 720.3470 -2.107
371.3643 -1.929 372.3974 -1.547 720.3484 -2.043
371.3661 -1.933 372.3995 -1.531 720.3499 -2.036
371.3679 -1.884 372.4016 -1.522 720.3513 -1.965
371.3696 -1.873 372.4038 -1.547 720.3528 -2.041
371.3714 -1.826 372.4059 -1.582 720.3542 -1.974
371.3732 -1.839 372.4080 -1.609 720.3557 -1.910
371.3750 -1.768 372.4101 -1.570 720.3571 -1.914
371.3767 -1.722 372.4123 -1.688 720.3586 -1.915
371.3785 -1.641 372.4172 -1.749 720.3600 -1.845
371.3803 -1.642 372.4193 -1.796 720.3615 -1.872
371.3821 -1.628 372.4214 -1.840 720.3629 -1.780
371.3838 -1.627 372.4235 -1.887 720.3643 -1.800
371.3856 -1.600 372.4257 -1.904 720.3658 -1.693
371.3874 -1.521 372.4278 -1.948 720.3672 -1.694
371.3892 -1.557 372.4299 -1.961 720.3687 -1.654
371.3910 -1.537 372.4320 -1.990 720.3701 -1.675
371.3927 -1.598 372.4342 -2.004 720.3716 -1.604
371.3945 -1.626 372.4363 -2.097 720.3730 -1.547
371.3963 -1.634 372.4384 -2.066 720.3745 -1.590
371.3981 -1.687 372.4405 -2.100 720.3759 -1.567
371.3998 -1.709 372.4427 -2.149 720.3773 -1.550
371.4016 -1.730 372.4448 -2.083 720.3788 -1.595

Table 2: Continued
HJD-2452000   HJD-2452000   HJD-2452000
371.4034 -1.788   372.4469 -2.119   720.3802 -1.547
371.4052 -1.798   372.4490 -2.111   720.3817 -1.584
371.4069 -1.835   372.4511 -2.087   720.3831 -1.615
371.4087 -1.887   372.4533 -2.137   720.3846 -1.702
371.4105 -1.927   372.4554 -2.113   720.3860 -1.681
371.4137 -1.952   372.4575 -2.183   720.3875 -1.670
371.4158 -1.976   372.4597 -2.125   720.3889 -1.672
371.4179 -1.986   372.4618 -2.140   720.3903 -1.841
371.4201 -2.020   372.4639 -2.200   720.3918 -1.717
371.4222 -2.005   372.4660 -2.150   720.3932 -1.829
371.4243 -2.060   372.4681 -2.199   720.3947 -1.859
371.4264 -2.097   372.4703 -2.193   720.3961 -1.849
371.4286 -2.080   372.4724 -2.201   720.3976 -1.896
371.4307 -2.078   372.4745 -2.184   720.3990 -1.923
371.4328 -2.101   372.4766 -2.165   720.4005 -1.994
371.4349 -2.149   372.4788 -2.189   720.4019 -2.010
371.4371 -2.117   372.4809 -2.216   720.4034 -2.072
371.4392 -2.110   372.4830 -2.187   720.4048 -2.026
371.4413 -2.142   372.4852 -2.218   720.4063 -2.004
371.4434 -2.179   372.4873 -2.189   720.4077 -2.041
371.4456 -2.162   372.4894 -2.179   720.4091 -2.069
371.4477 -2.167   372.4915 -2.211   720.4106 -2.116
371.4498 -2.186   372.4936 -2.212   720.4120 -2.129
371.4519 -2.181   372.4958 -2.169   720.4135 -2.124
371.4541 -2.213   372.4979 -2.213   720.4149 -2.094
371.4562 -2.161   372.5000 -2.173   720.4164 -2.167
371.4583 -2.187   386.3375 -2.272   720.4178 -2.157
371.4604 -2.229   386.3392 -2.237   720.4193 -2.184
371.4626 -2.216   386.3409 -2.246   720.4207 -2.183



Footnotes

... package1
The Mira AP software is produced by Mirametrics Inc.





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